Solution of plasticized cellulose acetobutyrate and fabrics coated therewith



leaned? s UNI rrrcruznsor. lvltiiiiliii DFFICE SULUTION OF PLASTICIZED CELLULOSE ACETGB'UTYRATE AND FABRICS COAT- ED THEREWITH Howard A. Gray, Nahant, Masa, assignor to Monsanto Chemical Company, St. Louis, Mo acorporation of Delaware No Drawing. Application August 20, 1946, Serial No. 691,87 9

12 Claims.

The present invention relates to coating compositions for use as aeroplane dopes. More particularly, this invention relates to the preparation and application of improved aeroplane dopes comprising cellulose aceto-butyrate in conjunction with certain solvents and modifiers thereof.

An object of the present invention is to provide an aeroplane dope which, upon application to the aeroplane fabric, provides improved characteristics thereto.

A further object of this invention is to provide an aeroplane dope which, upon application to the fabric of an aeroplane, provides a surface having improved fire resistance, improved resistance to ultra violet light and which possesses marked durability.

Other and further objects of the invention will be apparent as hereinafter described.

In the construction of many types of aeroplanes, cloth of a certain type is employed extensively for covering wing, fuselage, tail and other surfaces of the aeroplane. To furnish a satisfactory product, such cloth is covered with coating composition, and the coated fabric must not only possess great strength, but preferably must be relatively non-inflammable, resistant to ultra violet light, and must be durable; that is, resistant to weathering and abrasion as well as the impact effect of small particles, such as sand and gravel and the like. As is apparent, the

coated fabric must likewise possess sufiicient strength to resist the stress and strain placed upon it when in place on the aeroplane. It also must have such dimensional stability as to retain satisfactory tautness under general operating conditions of an aeroplane.

In order to waterproof the aeroplane fabrics and also to cause them to set tightly on the frame of the aeroplane after they are attached thereto, the fabrics are usually coated with conpositions having as abasis a derivative of cellulose which may form a smooth waterproof film thereon. Heretofore, aeroplane dopes comprised more generally compositions containing cellulose nitrate or cellulose acetate. However, aeroplane coating compositions or dop-es comprising cellulose nitrate or cellulose acetate, both of which have been used heretofore, have many drawbacks. Thus, coatings made from cellulose nitrate dopes are highly inflammable, while coatings made from cellulose acetate dopes are highly hygroscopic with their accompanying disadvantages. Furthermore, neither-of these dopes possess the required resistance to ultra violet light and durability.

In accordance with the present invention, it has been found that a particularly improved aeroplane dope is provided by employing cellulose aceto-butyrate as a basis and the addition thereto of a mixture of particular solvents, in the manufacture and use of which the formation of stock solutions are not necessary, but, on the contrary, the solution of the cellulose acetobutyrate may be prepared ready for application to the aeroplane fabric with the accompanying desirable results as hereinafter shown. Such a solvent mixture has as a primary component thereof a lower nitroparaflin, such as, for example, l-nitropropane and Z-nitroDropane. Complementary to the nitroparaiiin a lower aliphatic ketone, such as, for example, methyl ethyl ketone, is added. Butyl alcohol also may be added. Plasticizers, for example, triphenylwphosphate, are also incorporated in the ope. In order to further increase the durability of the preferred aeroplane fabric coating composition, it has been found desirable to incorporate relatively small proportions of phenyl salicylate therein.

The dopes of the present invention are substantially free from blushing even when drying in an atmosphere of. relatively high humidity, such as, for example, to relative humidity at 70 F., and aeroplane fabrics to which they are applied are not only possessed of great strength, but are relatively non-inflammable, resistant to ultra violet light, weathering, abrasion and have such dimensional stability so as to retain satisfactory tautness under general operating conditions of an aeroplane.

As a specific embodiment of the invention, an aeroplane dope was prepared comprising the following composition:

Per cent Methyl ethyl ketone 24.0 l-nitropropane 51. Butyl alcohol 10.0 Triphenyl phosphate 2.6 Phenyl salicylate 0.3 Cellulose aceto-butyrate 11.7

(Acetyl content 30 -33%, butyryl content method of application is employed, it is generally necessary to add somewhat varied amounts of ketone and nitropropane. Thus, a convenient aeroplane coating composition for cold application is made from about 80 parts by weight or" the above composition and adding thereto about 20 parts by weight of a mixed solvent comprising about 80 parts by weight of methyl ethyl ketone and about 20 parts by weight of l-nitropropane. The resulting composition may be applied by either the brush or spray method.

By means of the coating composition of the present invention, excellent flow characteristics are exhibited, in consequence of which, a coating 6 to 8 mils in thickness may be obtained from coats when applied with normal cold application. When applied by the hot spray method. the same material will lay down this thickness of film in 4 coats. It has been customary heretofore to apply 8 to 14 coats in order to obtain a film of comparative thickness.

As a specific example of this invention, 4 coats of the above dope were applied by the hot spraying method to a test panel 15" x 15" on which aeroplane fabric was fastened and stretched in the usual way to simulate an aeroplane wing. After exposure, the fabric was found to have retained, to a remarkable degree, its original tensile and other characteristics for from two to three times as long as fabric coated with a cellulose nitrate dope.

As a further specific example of this invention, 5 coats of the above dope, as modified for cold application, were applied cold for testing purposes to control surfaces of a commercial air transport aeroplane. After 17 months of commercial service these surfaces to which were applied the composition of this invention were still in serviceable condition. having retained to a remarkable degree their original characteristics. It is thus apparent that a marked advance has been made in the art of manufacture of coating composition or dopes and their application to surfaces, and more particularly fabric surfaces, such as, aeroplane wings, aeroplane controls and the like.

As hereinbefore set forth in the preferred embodiment of the invention, relatively small proportions of phenyl salicylate. for example, about 0.1% to about 0.5%, based on the weight of the coating composition, are preferably added thereto. An increase in durability of the aeroplane fabric coated with the dopes of the present invention containing phenyl salicylate over that where phenyl salicylate is not added, of from about one-half to two-thirds was obtained.

The ratios of the complementary solvents, the ketones and the nitroparafiin, may be varied. Thus, the nitroparafiin, such as l-nitropropane, comprises preferably from about 35% to about 60% of the weight of coating composition. When employed in higher quantities, a composition possessing poor drying properties is obtained; when employed in lower quantities, poor levelling and blushing results. The ketone, such as methyl ethyl ketone, comprises preferably from about 15% to about 40% of the weight of the coating composition. When less than this lower amount is employed, sufilcient solids cannot be incorporated in order to reduce the number of coats to that to which the dope of this inven tion is adapted. If larger amounts of the ketone are employed, blushing in humid weather takes place, It is thus apparent that the quantities of these complementary solvents influence and determine markedly the characteristics of the dope. The quantity of the butyl alcohol, which is not, however, a true solvent for the cellulose aceto-butyrate, may likewise be varied somewhat. Generally, from about 5% to 15% of the total weight of the coating composition may be employed. Again, the quantity of plasticizer, such as triphenyl phosphate, may be varied, preferably from between about 1.5% to about 3.5% of the total weight of coating composition. Again, the quantity of cellulose aceto-butyrate in the coating composition may be varied, Thus. a quantity of cellulose aceto-butyrate, preferably between about 6% to 13%, based on the total weight of the coating composition, may be employed. Of course, the various pigments may be employed if desired. Likewise, mildewproofing agents may also be incorporated in the coating composition.

As hereinbefore set forth, the coating composition or aeroplane dope of this invention has great flame resistance. Thus, when a Bunsen burner with air shut off and flame 4 inches long is held at a 30 degree angle in contact with the aeroplane fabric coated with the dopes of this invention, the coated fabric will burn only so long as the flame is in contact with it. When the flame is removed, the fire goes out.

The above examples are to be understood as illustrative and not limitative of the scope of the present invention.

What is claimed is:

1. A coating composition or dope for coating aeroplane fabric comprising substantially from 6% to 13% cellulose acetobutyrate, 40% to 15% methyl ethyl ketone, 35% to 60% l-nitropropane, 5% to 15% butyl alcohol, 1.5% to 3.5% triphenyl phosphate and 0.1% to 0.5% phenyl salicylate.

2. A coating composition or dope comprising cellulose acetobutyrate and a mixed true solvent therefor consisting of from 35% to 60% of a lower nitroparaffin and from 40% to 15% of a lower aliphatic ketone, said percentages being by weight and based on the coating composition.

3. An aeroplane fabric coated with a film formed from a composition comprising substantially from 6% to 13% cellulose acetobutyrate, 40% to 15% methyl ethyl ketone, 35% to 60% l-nitropropane, 5% to 15% butyl alcohol, 1.5% to 3.5% triphenyl phosphate and 0.1% to 0.5% phenyl salicylate, said film being characterized by its durability. fire and ultraviolet light resistanoe and resistance to blushing during drying.

4. A coating composition or dope comprising from 6 to 13% of cellulose acetobutyrate, a plasticizer therefor and a mixed true solvent for said cellulose acetobutyrate consisting of from 35% to 60% of a lower nitroparafiin and from 40 to 15% of methyl ethyl ketone, said percentages being by weight and based on the coating composition.

5. A coating composition or dope comprising (1) from 6 to 13% of cellulose acetobutyrate, (2) a mixed true solvent therefor consisting of from 35% to 60% of a lower nitroparaffin selected from the group consisting of l-nitropropane and Z-ni" tropropane and from 40 to 15% of methyl ethyl ketone, (3) from 5 to 15% of butyl alcohol and (4) from 1.5 to 3.5% of a plasticizer for said cellulose acetobutyrate, said percentages being by weight and based on the coating composition.

6. A coating composition or dope comprising (1) from 6 to 13% of cellulose acetobutyrate, (2) a mixed true solvent therefor consisting of from 35 to 60% of l-nitropropane and from 40 to 15% eras ate of methyl ethyl ketone, (3) from 5 to 15% of butyl alcohol and (4) from 1.5 to 3.5% of a plasticizer for said cellulose acetobutyrate, said percentages being by weight and based on the coating composition.

'7. A coating composition or dope comprising (1) from 6 to 13% of cellulose acetobutyrate, (2) a mixed true solvent therefor consisting of from 35 to 60% of l-nitropropane and from 40 to 15% of methyl ethyl ketone, (3) from 5 to 15% of butyl alcohol, (4) from 1.5 to 3.5% of a plasticizer for said cellulose acetobutyrate and (5) from 0.1 to 0.5% of phenyl salicylate, said percentages being by weight and based on the coating composition.

8. A coating composition or dope comprising (1) from 6 to 13% of cellulose acetobutyrate, (2) a mixed true solvent, therefor consisting of from 35 to 60% of a mixture of l-nitropropane and 2- nitropropane and from 40 to 15% of methyl ethyl ketone, (3) from 5 to 15% of butyl alcohol, (4) from 1.5 to 3.5% of triphenyl phospate and (5) from 0.1 to 0.5% of phenyl salicylate.

9. An aeroplane fabric coated with a film formed from a composition comprising cellulose acetobutyrate and a mixed true solvent therefor consisting of from 35 to 60% of a lower nitroparafiln and from 40 to 15% of a lower aliphatic ketone, said percentages being by weight and based on the coating composition, said film being characterized by its durability, fire and ultra-violet light resistance and resistance to blushing during drying.

10. An aeroplane fabric coated with a film formed from a composition comprising cellulose acetobutyrate, a plasticizer therefor and a mixed true solvent for said cellulose acetobutyrate consisting of from 35 to 60% of a lower nitroparaflin and from 40 to 15% of methyl ethyl ketone, said percentages being by weight and based on the coating composition, said film being characterized by its durability, fire and ultra-violet light resistance and resistance to blushing during drymg.

11. An aeroplane fabric coated with a film formed from a composition comprising (1) from 6 to 13% cellulose acetobutyrate, (2) a mixed true solvent therefor consisting of from 35 to of a substance selected from the group consisting of l-nitropropane and Z-nitropropane, and from 40 to 15% of methyl ethyl ketone, (3) from 5 to 15% of butyl alcohol and (4) from 1.5 to 3.5% of a plasticizer for said cellulose acetobutyrate, said percentages being by weight and based on said coating composition, said film being characterized by its durability, fire and ultra-violet light resistance and resistance to blushing during drying.

12. An aeroplane fabric coated with a film formed from a composition comprising (1) from 6 to 13% of cellulose acetobutyrate, (2) a mixed true solvent therefor consisting of from 35 to 60% of i-nitropropane and from 40 to 15% of methyl ethyl ketone, (3) from 5 to 15% of butyl alcohol, (4) from 1.5 to 3.5% of a plasticizer for said cellulose acetobutyrate and (5) from 031 to 0.5% of phenyl salicylate, said percentages being by weight and based on said coating composition, said film being characterized by its durability, fire and ultra-violet light resistance and resistance to blushing during drying.

HOWARD A. GRAY.

REFERENCES CITED The following references are of record in the OTHER REFERENCES Hercules: Cellulose Acetate (1943), page 10. Hercose C (1941), pages 12 and 13.

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2. A COATING COMPOSITION OR DOPE COMPRISING CELLULOSE ACETOBUTYRATE AND A MIXED TRUE SOLVENT THEREFOR CONSISTING OF FROM 35% TO 60% OF A LOWER NITROPARAFFIN AND FROM 4% TO 15% OF A LOWER ALIPHATIC KETONE, SAID PERCENTAGES BEING BY WEIGHT AND BASED ON THE COATING COMPOSITION. 